Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: A escola de Portage estava em qual conferência anteriormente?
 ###Tabelas: CREATE TABLE current_members (current_members_id AUTO_INCREMENT PRIMARY KEY, School VARCHAR, Location VARCHAR, Mascot VARCHAR, County VARCHAR, Enrollment 08-09 INT, IHSAA Class VARCHAR, IHSAA Class Football VARCHAR, Year Joined INT, Previous Conference VARCHAR) CREATE TABLE 1969_as_three_leagues_come_together (1969_as_three_leagues_come_together_id AUTO_INCREMENT PRIMARY KEY, Portland DFL VARCHAR, Wins INT, Byes INT, Losses INT, Draws INT, Against INT) CREATE TABLE regional (regional_id AUTO_INCREMENT PRIMARY KEY, Branding VARCHAR, Callsign VARCHAR, Frequency VARCHAR, Power (kW) VARCHAR, Location VARCHAR) CREATE TABLE average_crowd_sizes (average_crowd_sizes_id AUTO_INCREMENT PRIMARY KEY, Season VARCHAR, Ave. Attendance INT, +/- ave. on prev. season VARCHAR, Competition VARCHAR, Occupier VARCHAR) CREATE TABLE detailed_olympic_results (detailed_olympic_results_id AUTO_INCREMENT PRIMARY KEY, Year INT, Competition Description VARCHAR, Location VARCHAR, Apparatus VARCHAR, Score-Final INT, Score-Qualifying INT)  
SELECT Previous Conference FROM current_members WHERE School = portage